Autodesk 123D - Free 3D Modeling Software, 3D Models, DIY Projects, Personal Fabrication Tools
Autodesk has a beta of a new 3D program which is free for now (and supposedly free after beta as well). It looks to be a cross between the free Google SketchUp and parametric apps such as Solidworks and Inventor, and it is designed to create output ready to be made by rapid prototyping via .STL export.
Since it is in beta, it would be great to see if we could convince them to also include simple 2.5D CAM-type features as well, such as outline extraction for 2.5D toolpaths from model features. If they could add some basic intelligence such as tool information and machining ops in the model tree, it could make G-Code conversion much simpler and more conducive to revision. For example, if a hole feature had an attribute that allowed it to be recognized as something appropriate for a drill operation, it would be dead-simple to produce G-Code that would automatically update if the hole was moved.
Or, I could see clicking on a chamfer feature and entering a tool diameter for a bevel cutter; and a toolpath could be inferred at the appropriate Z level and X-Y offset to cut the chamfer efficiently, instead of simply outputting a 3D solid that you would have to "deconstruct" in a separate CAM program to build the appropriate machining ops. Since they seem to be orienting this product towards creating models destined to be easily made, perhaps they might be receptive to building in some extra capability that would make simple CAM operations much easier and more revision-friendly.
A big barrier to entry for hobby (or even commercial) CNC is the requirement to get proficient in a whole bunch of software - CAD to draw your part, exporting in the appropriate format, importing to CAM, producing G-Code, and then bringing it into the CNC control. It sure would be nice if we could condense a lot of those functions into one program that would make it easy to change things without having to start over.
I have downloaded and installed it, but haven't played with it much yet; but it looks promising. And for free, it's definitely worth checking out.